Gas Blending

The process of mixing breathing gases such as nitrox and trimix to a target composition, then verifying the result with an oxygen analyzer.

Gas blending is the craft of producing breathing mixes such as nitrox and trimix to a planned composition. The most common method is partial pressure blending: the blender adds pure oxygen, and helium if needed, to a calculated pressure, then tops the cylinder with air, using Dalton's law to hit the target fractions. Alternatives include continuous blending, where oxygen is injected into the compressor intake stream, and membrane systems that strip nitrogen from air.

Precision and safety dominate the process. Cylinders and whips that see rich oxygen must be oxygen clean, oxygen must be added slowly to limit heat, and every finished mix is verified with a calibrated oxygen analyzer before it leaves the fill station. Temperature matters too: a freshly filled warm cylinder reads a different pressure once it cools, so good blenders let mixes settle before final analysis.

Blending is its own certification, with separate ratings for nitrox and trimix blending at most technical agencies. Divers do not need the card, but the habit it teaches applies to everyone: personally analyze every tank you breathe, compare the reading against what you ordered, and label the cylinder with the mix and its maximum operating depth before it ever gets near the water.